The present invention relates to security printing inks used to thwart counterfeiting of printed commercial documents such as sales transaction records and receipts.
Many different means of security are available to prevent duplication of printed commercial documents such as special papers (water marked paper) and special inks (fluorescent inks and other optically variable inks) which form latent images or images that change color.
The use of latent images as a security measure is well known. To be useful as a security measure, latent images must be well camouflaged but readily and easily viewable to the user, preferably by a simple procedure. An example of such a latent image is described in U.S. Pat. No. 5,468,581, which is formed when printing documents using an intaglio process. The latent image is overprinted on the visible image such that the latent image is visible when the document is tilted and viewed at an angle. The latent image is caused by the variation of the slight shadow from the raised ink pattern formed by the intaglio process or other printing method which produces raised ink patterns. This technique is not well suited for other printing methods, such as ink jet printing and thermal transfer printing, which do not typically provide raised ink patterns and do not easily incorporate the steps necessary to vary the shadows formed by such raised ink patterns.
Optically variable inks have been used to provide latent images and images which change color when exposed to a light source other than ambient light. Such optically variable inks typically contain a fluorescent compound or photochromic compound which responds to infrared or ultraviolet light. An example of an aqueous printing ink for jet printing which fluoresces under ultraviolet radiation is described in U.S. Pat. No. 4,153,593. The dyes described in this reference are water soluble and include fluorescein, eosine dyes and Rhodamine dyes. Fluorescent pigments and dyes for use in water-based jet printing inks are well known. Representative disclosures include U.S. Pat. No. 4,328,332, issued to Hayes et al. on May 4, 1982, and U.S. Pat. No. 4,150,997, issued to Hayes on Apr. 24, 1979. While the use of fluorescent inks and dyes has been effective and versatile, with the advent of today""s personal computers and color copiers, conventional security measures such as these have been overcome, particularly where records are only casually inspected, such as sales receipts and transaction records. Therefore, it is desirable to provide additional security measures to supplement the fluorescent pigments and dyes.
Adding additional security measures is complicated by many factors. One is that there are many types of printing inks with compositions adapted to be employed in particular printing operations. For example, the inks for ink jet printers must be conductive, have viscosity values within a certain range and contain no large particulate matter (below 5 mm) and the ink should not dry within the ink jet over short periods of time.
Jet printing processes are described in Report No. 1722-1 of the Stanford University Electronic Research Laboratory dated March 1964, entitled xe2x80x9cHigh Frequency of Oscillography with Electrostatically Deflected Ink Jetsxe2x80x9d. The basic imaging technique involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each jet includes a small orifice usually having a diameter in the order of about 0.0024 in. Which is electromagnetically energized to emit a continuous stream of uniform droplets of ink. This stream of droplets is directed onto a moving surface, for example, a moving web of paper and is controlled to form printed characters. (See, for example, U.S. Pat. Nos. 3,596,275; 4,269,627; 4,153,593; 4,328,332; and 4,150,997.)
Inks for thermal transfer printing must have softening/melting points enabling flow and tackiness enabling adhesion to a receiving substrate under the operating conditions of a thermal transfer printer. In thermal transfer printing, images are formed on a receiving substrate by heating extremely precise areas of a print ribbon with thin film resistors. The print ribbon comprises a supporting substrate and a functioning layer or xe2x80x9cink layerxe2x80x9d. Heating of the localized area causes transfer of the ink layer or functional layer from the ribbon to the receiving substrate. The functional layer or ink layer contains the requisite pigment or dye which enables detection either visually, optically or magnetically. See U.S. Pat. No. 3,663,278, issued May 16, 1972 and U.S. Pat. Nos. 4,315,643; 4,403,224; 4,687,701; and 5,240,781.
Special ink formulations are also employed in relief printing, offset printing, intaglio printing, lithography and silk screening.
Another factor which complicates adding a security measure to a security ink is that water-based inks are preferred to minimize the impact on the environment and avoid flammable vapors during use. This limits the components that can be added to the security ink.
An additional factor which complicates adding a security measure to a security ink is that it is difficult to complement the performance of fluorescent and photochromic pigments and dyes within optically variable inks without interfering with their performance. Parameters such as these place limitations on the additives or other components which can be used with security inks, making it difficult to provide multiple security measures within a security ink.
It is an object of the present invention to provide a printing ink with two forms of security to prevent counterfeiting.
It is another object of the present invention to provide a water-based security ink with a new security measure for determining counterfeit documents.
It is another object of the present invention to provide a security ink with a security measure for determining counterfeit documents which can complement the use of conventional security measures with optically variable pigments and dyes such as thermochromic, photochromic and fluorescent pigments and dyes.
It is another object of the present invention to provide jet printing inks and other water based inks with two security measures.
It is another object of the present invention to provide an imaged substrate with two modes of security ink with a security mechanism that works in tandem with fluorescent, thermochromic and photochromic pigments and dyes.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent and further understood from the detailed description and claims which follow.
The above objects are achieved through the use of a water-based security printing ink which comprises a water soluble, dispersible or emulsifiable pigment or dye with variable light absorption and/or transmission properties, a carrier for said pigment or dye selected from aqueous solutions and water soluble, dispersible or emulsifiable binders and a water repelling agent in an amount sufficient to render the ink waterproof once dried. This printing ink provides two modes of security, one through the variable light absorption and/or transmission properties and the other through its waterproof properties. Thermal transfer ribbon ink and jet printing ink which contain these two modes of security are included in this invention.
In another aspect of the present invention, there is provided imaged substrates having a waterproof image printed thereon which comprises a water soluble, dispersible or emulsifiable pigment or dye with variable light absorption and/or transmission properties, a water soluble, dispersible or emulsifiable binder for said pigment or dye and a water repelling agent in an amount sufficient to render the image waterproof.